1. Field of the Invention
Systems and methods consistent with the present invention relate to a wireless communication for reducing a ranging time. More particularly, the present invention relates to a wireless communication method and a wireless communication system with a reduced ranging time for shortening a synchronization process by separating the synchronization process into a plurality of phases and determining whether a received signal is ranging communication or data communication.
2. Description of the Related Art
The Institute of Electrical and Electronics Engineers (IEEE) 802.15.4 standard has suggested a full function device (FFD) and a reduced function device (RFD). The FFD performs wireless communications with other devices without a separate intermediate entity, and the RFD performs wireless communications only via an intermediate entity such as the FFD.
Localization is a technique to acquire a position of a device using the communications with other devices. Ranging is a process conducted on the physical layer to measure a relative distance between two devices.
The IEEE 802.15.4a standard meeting has adopted the ranging technique as an obligatory technique, and the spirited discussion is made on whether the ranging technique has a protocol. In case there is a protocol, a transmitting device which intends to measure a distance is assigned a channel and measures a relative distance by transmitting and receiving a radio frequency (RF) signal for the ranging to and from a receiving device through the assigned channel. In case there is no protocol, the transmitting device performs the synchronization of the RF signal and measures the distance to the receiving device under a certain assumption without utilizing the protocol.
If the ranging technique is applied to an ultra wide band (UWB) system, in practice, the transmitting device that intends to measure the distance needs to consider accuracy, measurement time, hardware complexity, and power consumption of the distance measurement. Particularly, the fast distance measurement is required when the measurement is needed to promptly cope with an emergency such as a fire, a disaster, and a military event, or when the device is mobile.
Various patent applications and papers have proposed methods to rapidly measure the distance between devices.
In the paper entitled “A Two Step Time of Arrival Estimation Algorithm for Impulse Radio Ultra Wideband Systems”, Mitsubishi Electric Research Lavatories Inc., 2005, the synchronization is performed during the ranging under the assumption that the synchronization is flawless.
The paper describes that the synchronization is performed and then the ranging is conducted after the synchronization without utilizing a protocol. As a result, the time taken for the synchronization increases.
Meanwhile, in a ranging method in conformity with a protocol, the ranging is carried out by repeatedly transmitting a signal in a channel occupied according to the protocol. Since the ranging protocol is suggested in the upper layer, it is required to transmit and receive a signal to prepare for the ranging in conformity with the ranging protocol in the distance measurement In brief, some time is required to prepare for the ranging.
Accordingly, the ranging time is likely to increase because the methods described in the patent applications and the papers of the related art need to perform the synchronization with respect to ranging techniques that do not utilize the protocol, and to transmit and receive the signal before the ranging with respect to the ranging techniques that utilize the protocol.
Typically, the synchronization discriminates a desired signal of the transmitting device from noise among several signals received from the receiving device, and arranges for the recovery of the received signal by detecting a start point and the end point of a symbol.
However, the discrimination between the desired signal and the noise is required both in the ranging and the data communications, whereas the detection of the start point and the end point of the symbol is required only in the data communications.
If it is possible to separate the detection of the start point and the end point of the symbol from the synchronization, the detection of the start point and the end point of the symbol can be executed in the data communications without detecting the start and end points of the symbol in the ranging. That is, the ranging time can be reduced.